A008335 Number of distinct primes dividing p+1 as p runs through the primes.

1, 1, 2, 1, 2, 2, 2, 2, 2, 3, 1, 2, 3, 2, 2, 2, 3, 2, 2, 2, 2, 2, 3, 3, 2, 3, 2, 2, 3, 3, 1, 3, 3, 3, 3, 2, 2, 2, 3, 3, 3, 3, 2, 2, 3, 2, 2, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 2, 2, 3, 2, 3, 3, 3, 2, 3, 2, 2, 3, 3, 3, 3, 2, 3, 3, 2, 4, 2, 3, 3, 4, 2, 2, 3, 3, 3, 3, 2, 4, 2, 3, 3, 2, 3, 2

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

• T. D. Noe, Table of n, a(n) for n=1..10000

Crossrefs

Cf. A001221, A008864, A023514.

Programs

Maple

for i from 1 to 500 do if isprime(i) then print(nops(factorset(i+1))); fi; od;

Mathematica

a[n_] := PrimeNu[Prime[n]+1]; Array[a, 100] (* Amiram Eldar, Sep 10 2024 *)

PARI

a(n) = omega(prime(n)+1); \\ Michel Marcus, Mar 29 2016

Formula

a(n) = A001221(A008864(n)). - Michel Marcus, Mar 29 2016